P129B

DTC P129B

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Diagnostic System Check - Vehicle) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Strategy Based Diagnosis) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Diagnostic Procedure Instructions) provides an overview of each diagnostic category.

DTC Descriptor
DTC P129B
- System Voltage Low - FPDM

Diagnostic Fault Information





Circuit/System Description

The fuel pump control module (FPCM) monitors the system voltage supplied to the fuel pump driver module (FPDM) to ensure that the voltage stays within the proper range. Damage to components, and incorrect data may occur when the voltage is out of range.

Conditions for Running the DTC

The engine is running.

Conditions for Setting the DTC

The FPCM detects that the battery voltage supplied to the FPDM is less than 9 V for 5 seconds.

Action Taken When the DTC Sets

DTC P129B is a type A DTC.

Conditions for Clearing the DTC

DTC P129B is a type A DTC.

Reference Information
Schematic Reference

Engine Controls Schematics (LS3) ([1][2]Electrical Diagrams) Engine Controls Schematics (LS7) ([1][2]Electrical Diagrams) Engine Controls Schematics (LS9) ([1][2]Electrical Diagrams)
Connector End View Reference

Component Connector End Views (Connector Views)
Description and Operation

Charging System Description and Operation (Description and Operation)
Electrical Information Reference

* Circuit Testing (Circuit Testing)
* Connector Repairs (Connector Repairs)
* Testing for Intermittent Conditions and Poor Connections (Testing For Intermittent Conditions and Poor Connections)
* Wiring Repairs (Wiring Repairs)

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (Powertrain Diagnostic Trouble Code (DTC) Type Definitions)
Scan Tool Reference

Control Module References (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Engine running, accessories OFF, measure and record the battery voltage at the battery terminals. The voltage should be between 12.6 and 15.0 V.

• If not within the specified range, refer to Charging System Test (Charging System Test).

2. Ignition OFF, disconnect the harness connectors at the FPDM.
3. Ignition OFF and scan tool disconnected, open and close the driver door, and wait 1 minute. Test for less than 5 Ohms between the ground circuit terminal 5 X1 and ground.

• If greater than the specified range, test the ground circuit for an open/high resistance.

4. Verify that a test lamp illuminates between the B+ circuit terminal 3 X1 and ground.

• If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

5. Ignition ON, verify that a test lamp illuminates between the ignition circuit terminal 5 X2 and ground.

• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.

6. If all circuits test normal, replace the Fuel Pump Flow Control Module Relay.

Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

Refer to Fuel Pump Flow Control Module Relay Replacement (Service and Repair) for Fuel Pump Flow Control Module Relay.